CODEWITHSUNDEEP
matlabfunction
Nigel Overmars
Nigel Overmars

Reputation: 213

Matlab and functions

I feel incredible stupid that I have to ask this question, but everyone was a noob once. Right?!?

For an assignment we have to implement the following sum: PI - 3 = sum from i=1 to N of (-1)^(i+1) / i(i+1)(2i+1) (shame about the lack of Mathjax here)
So in Java:

public static double[] computeSumOfPi(int N) { //returns the value of PI computed
                                               //with N terms of the sum and the 
                                               //last added term
    double term = 0;
    double sum = 0;
    double[] result = new double[2];
    for(int i = 1; i < N + 1; i++) {
        term = Math.pow((-1),(i+1)) / i*(i+1)*(2*i+1);
        sum =  sum + term;
    }
    result[0] =  sum + 3;
    result[1] = term;
    return result;
}

In Matlab I tried the following

function [sumPi, lastTerm  ] = sumForPi( n )  %sumForPi.m
for i = 0 : n  
   term = (-1)^(i+1) / (i*(i + 1)*(2*i + 1));  
   temp = temp + term;   
end  
sumPi = temp + 3.0;  
lastTerm = term;  
end

Which I try to invoke:

>> sumForPi(20)

Which returns the following error:

undefined function or variable "temp"
Error in sumForPi (line 4)
temp = temp + term;

I would be delighted if someone could point out my (probably simple) mistake.

Thanks in advance!

Upvotes: 1

Views: 83

Answers (1)

tashuhka
tashuhka

Reputation: 5126

You need to declare the initial value of temp before you read it. Hence, try to include temp = 0; before the loop, i,e.

function [sumPi, lastTerm  ] = sumForPi( n )  %sumForPi.m
temp = 0;
for i = 0 : n  
   term = (-1)^(i+1) / (i*(i + 1)*(2*i + 1));  
   temp = temp + term;   
end  
sumPi = temp + 3.0;  
lastTerm = term;  
end

Upvotes: 2

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